Fuel assembly nozzleless handling tool and method

ABSTRACT

A device and method to move a fuel assembly of a nuclear reactor, wherein the device eliminates the potential for dropping the fuel assembly due to stress corrosion cracking of the upper guide thimble sleeves that attach the top nozzle to guide thimbles.

FIELD OF THE INVENTION

The current invention relates to handling of fuel assemblies for nuclearreactors. More specifically, the invention relates to a tool and methodfor movement of nuclear fuel assemblies without over stressing the topnozzle of the fuel assembly.

BACKGROUND INFORMATION

Present-day light water nuclear reactors, both pressurized waterreactors and boiling water reactors, require fuel to be installed in areactor pressure vessel prior to operation. The fuel is often in theform of a fuel assembly, where individual fuel rods, which contain aseries of parallel arranged rods each containing stacked pellets, areheld together by a structural skeleton arrangement.

After the reactor pressure vessel is operated and the nuclear fuel inthe fuel assemblies is depleted, the depleted fuel assemblies must beremoved and replaced with new fuel assemblies. Additionally,non-depleted fuel assemblies must be moved to other areas of the reactorcore and inspected for defects .prior to restarting the reactor. Themoving of the fuel assemblies, both depleted and non-depleted, must beperformed in a safe and-controlled manner as dropping of a fuel assemblycould lead to damage of nuclear fuel and potential release ofradioactive material.

Detailed visual and radiographic inspections of fuel assemblies andspecial lifting devices (devices that move the fuel assembly) helpprevent load lifting accidents due to degraded structural components. Ithas been found that after exposure to radiation, some fuel assembliesexhibit stress corrosion cracking of the upper guide thimble sleeveswhich attach the top nozzle of the fuel assembly to the guide thimbles.

Industry experience has also found that current devices and methods tolift structurally damaged fuel assemblies are costly for plantoperators, while not eliminating the potential for load liftingaccidents from problem prone areas such as failure of the top nozzle toguide thimble connection from stress corrosion.

If a fuel assembly exhibits stress corrosion cracking or some otherstructural defect, current practices require underwater disassembly ofthe fuel assembly and removal of the individual pieces or establishmentof additional structural corrections to the damaged fuel assembly toallow an adequate transfer of the structural load of the assembly. Bothof these repair alternatives are expensive and require significantstructural analysis of the damaged fuel assembly to ensure a safe loadlift.

There is a need for a fuel assembly lifting device and method which canbe used with existing fuel assembly configurations in nuclear reactors,both pressurized and boiling water reactors.

There is a further need to provide a fuel assembly lifting device andmethod which will allow for safe movement of a fuel assembly when thefuel assembly has stress corrosion cracking of the upper guide thimblesleeves that attach the top nozzle to the guide thimbles.

There is still further need for a device which will properly interfacewith existing fuel handling equipment and storage racks for costefficient effective movement of fuel assemblies.

SUMMARY

It is an objective of the present invention to provide a fuel assemblynozzleless handling tool and method which can be used with existingconfigurations of fuel assemblies used in nuclear reactors.

It is a further objective of the present invention to provide a fuelassembly nozzleless handling tool which will allow movement of a fuelassembly in a safe manner when the fuel assembly exhibits stresscorrosion cracking of the upper guide thimble sleeves that attach thetop nozzle to the guide thimbles.

It is a further objective of the present invention to provide a tool andmethod which will properly interface with existing fuel handlingequipment and storage racks for cost efficient and effective movement offuel assemblies.

The invention provides a method of handling a fuel assembly. The methodprovides for supporting a tool configured to handle the fuel assembly,and positioning the tool over a top of the fuel assembly. The methodfurther provides for lowering the tool onto the top of the fuel assemblysuch that alignment pins engage a top nozzle of the fuel assembly andactuating a shaft to lower lock fingers into guide thimbles of the fuelassembly. The method also provides for positioning the lock fingers to aposition below divots in the guide thimble in the fuel assembly to beengaged, engaging the lock fingers into the divots to an extendedposition, and lifting the fuel assembly and the tool.

The invention also provides a fuel assembly nozzleless handling toolconfigured to handle a fuel assembly. The tool comprises a mandrel shaftconfigured to travel a length of the tool. The tool also provides amandrel plate connected to the mandrel shaft, the mandrel plateconfigured to move through actuation of the mandrel shaft and a fingershaft configured to travel from an unengaged position to an engagedposition. The device further provides a finger plate configured toinsert and retract the lock fingers into the guide thimbles, the fingerplate moved by actuation of the finger shaft and a load plate. Thedevice still further provides at least two lock fingers configured tointerface with a fuel assembly guide thimble, and a mandrel for each ofthe two lock fingers, wherein the mandrel is configured to secure thelock fingers and retract the lock fingers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of a fuel handling nozzleless liftingtool in accordance with the present invention.

FIG. 2 is a side elevation view of the fuel handling lifting tool ofFIG. 1 wherein lock fingers are in an unextended position.

FIG. 3 is a side view of the fuel handling lifting tool of FIG. 1,wherein the mandrel shaft is lowered to extend the lock fingers.

DETAILED DESCRIPTION

FIG. 1 illustrates a fuel assembly nozzleless handling tool 10 inconformance with the present invention. The fuel assembly nozzlelesshandling tool 10 is comprised of a mandrel 14, a mandrel shaft 12, amandrel plate 16, a finger shaft 18, a lock finger 22, a finger plate 26and a load plate 24.

The fuel assembly nozzleless handling tool 10 is a device which allowsfor lifting of fuel assemblies which exhibit structural defects whichmay affect overall lifting safety. The handling tool 10, therefore,prevents the need for permanent structural repair from beingaccomplished on structurally degraded fuel assemblies.

The tool 10 interfaces with the existing structures in the fuel assembly20 in order to accomplish a load lift. To accomplish this, lock fingers22 are used to interface with fuel assembly guide thimbles. The externaldiameters of the lock fingers 22 are configured to allow insertion ofthe lock fingers 22 into the openings of the guide thimbles in the topnozzle. In the extended position, the ends or tabs of the lock fingers22 are configured to engage divots within the guide thimble where theguide thimble is swaged to the upper sleeve. The lock fingers 22 may befabricated from a variety of materials, including stainless steel orInconel. The lock finger ends or tabs may be in any configuration suchthat contact established between the lock fingers 22 and the dimples ofguide thimble is sufficient to allow a vertical lift of the fuelassembly 20. In an unextended position., the lock fingers 22 areconfigured to be inserted into the guide thimbles with sufficientclearance such that the lock fingers 22 do not contact the insidecontact edges of the guide thimbles. The ends of the lock fingers 22 maybe made of a material which is softer than the material of the guidethimbles, thereby preventing damage to the fuel assembly 20 in theextended position.

The mandrel 14 is used to secure the lock fingers 22 into place in afuel assembly 20 prior to lifting a fuel assembly 20. The mandrels 14also retract the lock fingers 22 to a smaller profile in the unengagedposition for insertion into the guide thimbles. The mandrels 14 areindividually spring loaded to their respective lock fingers 22 to allowindependent locking and unlocking of the lock fingers 22. The number ofmandrels 14 and lock fingers 22 may be varied according to the number ofconnections desired to be established to the fuel assembly 20 to belifted. In an exemplary embodiment illustrated, 20 lock finger/mandrelsare used to lift the fuel assembly 20. Other numbers of lockfinger/mandrels may be used according to the configuration of the fuelassembly 20 and the desired factor of safety for lifting.

The load plate 24 is configured to lift the weight of the fuel assembly20 transferred through the lock fingers 22. The lock fingers 22 aresupported with a spring interface by the load plate 24 to allow forvariation in fuel assembly growth and divot position. The load plate 24is attached to the mast 34 of the tool 10 via support rods 32 at eachcorner of the tool. Alignment pins 28 attach the load plate 24 toprovide accurate positioning onto the fuel assembly 20. The alignmentpins 28 may allow for fine adjustment of the tool 10 so that precisepositioning occurs.

The finger plate 26 is used to insert and retract the lock fingers 22into the guide thimbles of the fuel assembly 20. The finger plate 26 isa non-load bearing component and is connected to members 38 whichconnect to the mandrel plate 15 of the tool 10. The finger plate 26 mayhave an attachment 36 which allows/assists in the insertion andretraction of the lock fingers 22 during actuation.

The finger shaft 18 is configured to travel the full length of the fullassembly nozzleless handling tool 10 to allow operator movement of thefinger plate 26 via a screw drive 44. As illustrated, the finger shaft18 is a screw 40 which may be controlled in a precision manner. Thescrew 40 may be of such a configuration such that the threads of thescrew 40 allow for accurate positioning. The screw 40 may also beconfigured such that any configuration of threads per unit length may beused. Other types of actuation are possible, such as hydraulicactuation, for example, and as such the exemplary embodiment illustratedshould not be considered limiting.

The mandrel plate 16 is used to allow insertion and retraction of themandrels 14 into the lock fingers 22. The mandrel plate 16 is used toprovide a structural connection which may be actuated for movementthrough movement of the mandrel shaft 12. The mandrel plate 16 is alsoconfigured to allow visual verification that the mandrels 14 are fullyinserted through visual identification of position.

The mandrel shaft 12 travels the full length of the tool 10 to allowoperator movement of the mandrel plate 16 via rotation and elevationchange. The mandrel shaft 12 may be configured to rotate as illustrated,or may be moved through hydraulic actuation.

Operationally, control components for the reactor core and fuelassemblies are removed to provide access to the individual fuel assembly20 to be moved. The fuel assembly nozzleless handling tool 10 ispositioned over the fuel assembly 20 to be moved as illustrated in FIG.2. The fuel assembly nozzleless handling tool 10 is lowered onto thefuel assembly 20 and alignment pins 28 engage the top nozzle 30 of thefuel assembly 20. The finger shaft 18 is rotated by the tool operator tolower the lock fingers 22 into the guide thimbles of the fuel assembly20. The mandrel shaft 12 is then lowered by the operator to allow springtension of the mandrels 14 to be applied to the lock fingers 22. Thefinger shaft 18 is then rotated to perform a slow withdrawal of the lockfingers 22. As the individual lock fingers 22 reach divots that they areto engage, the lock fingers 22 spring into place, and the mandrel 14 istherefore positioned inside the guide thimble of the fuel assembly 20,locking a finger tab of the lock finger 22 into a divot of the guidethimble. The lock fingers 22 are withdrawn from the guide thimbles byactuation of the tool 10 until all of the mandrels 14 used are lockedinto position. Next, the mandrel shaft 12 is rotated to verify if all ofthe mandrels 14 are in the locked position and illustrated in FIG. 3.Finally, the fuel assembly nozzleless handling tool 10 is lifted by theauxiliary hoist of a fuel handling crane, as an example, and theassembly 20 is lifted and transferred to a new location.

The fuel assembly nozzleless handling tool 10 may be configured of anymaterial, such as stainless steel, that is corrosion resistant andprovides sufficient strength to lift the fuel assembly 20 with a desiredfactor of safety. The handling tool 10 is configured to engage guidethimble dimples below the upper end grid of the full assembly 20. Otherdimple areas in the guide thimble may be used, however, and theillustrated embodiment is but one alternative configuration. Althoughillustrated as a configuration that will attach to a 17×17 pressurizedwater reactor fuel assembly, the fuel assembly nozzleless handling tool10 could be reconfigured to fit any fuel assembly design that uses aswaged top nozzle sleeve.

The fuel assembly nozzleless handling tool 10 provides an alternative toexpensive and lengthy permanent fixes to damaged fuel assemblies. Thehandling tool 10 may be configured to be single failure proof whereinfailure of a single component on the handling tool 10 will not result inthe dropping of the assembly 20 during a load lift.

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments, thereof. It will, however,be evident that various modifications and changes may be made thereuntowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings areaccordingly to be regarded as an illustrative rather than a restrictivesense.

1. A method of handling a fuel assembly, comprising: supporting a toolconfigured to handle the fuel assembly; positioning the tool over a topof the fuel assembly; lowering the tool onto the top of the fuelassembly such that alignment pins engage a top nozzle of the fuelassembly; actuating a shaft to lower lock fingers into guide thimbles ofthe fuel assembly; positioning the lock fingers to a position belowdivots in the guide thimble in the fuel assembly to be engaged; engagingthe lock fingers into the divots to an extended position; and liftingthe fuel assembly and the tool.
 2. The method according to claim 1,further comprising: disengaging the tool from the fuel assembly.
 3. Themethod according to claim 1, wherein the shaft is rotated to lower thelock fingers into the guide thimbles.
 4. The method according to claim1, wherein the actuating of the shaft to lower the lock fingers isperformed by a mandrel shaft which allows a spring tension to be appliedto the lock fingers.
 5. A fuel assembly nozzleless handling toolconfigured to handle a fuel assembly, comprising: at least four supportrods; a mandrel shaft configured to travel a length of the tool; amandrel plate connected to the mandrel shaft, the mandrel plateconfigured to move through actuation of the mandrel shaft; a fingershaft configured to travel from an unengaged position to an engagedposition; at least two lock fingers configured to interface with a fuelassembly guide thimble; a finger plate configured to insert and retractthe lock fingers into guide thimbles, the finger plate moved byactuation of the finger shaft; a load plate connecting to the supportrods the load plate configured to receive an end of the finger shaft;and a mandrel for each of the at least two lock fingers, wherein themandrel is configured to secure the at least two lock fingers andretract the at least two lock fingers.
 6. The device according to claim5, wherein the lock finger is configured to engage divots in the guidethimble.
 7. The device according to claim 5, wherein the mandrel isconfigured with springs to allow independent locking of individual lockfingers.
 8. The device according to claim 5, further comprising: atleast four support rods connected to the load plate, each of the atleast four support rods positioned at a corner of the load plate.
 9. Thedevice according to claim 5, wherein the load plate is configured witharrangements to accept alignment pins of the fuel assembly.
 10. Thedevice according to claim 5, wherein the lock fingers are configured tobe inserted into the fuel assembly where a guide thimble is swaged to anupper sleeve.
 11. The device according to claim 5, wherein the lockfingers are made of stainless steel.
 12. The device according to claim5, wherein the lock fingers are made of Inconel.
 13. The deviceaccording to claim 5, further comprising: alignment pins configured toengage a top nozzle of the fuel assembly, the alignment pins at a bottomof the tool.
 14. The device according to claim 5, wherein the lockfingers are configured with tabs to engage divots of the fuel assembly.15. The device according to claim 5, wherein the tool has 20 lockfingers and 20 mandrels.